Dust removal devices

Besides bubbling—vortical gas washer can be used as the independent dust removal device, and to be established installed in vent dust removal system with the purpose of economy of material means and the areas of industrial premises rooms. ... 

The cleaning cycles are usually controlled by a timing device which deactivates the section being cleaned. The dusts removed during cleaning are collected in a hopper at the bottom of the baghouse and then removed, through an air lock or star valve, to a bin for ultimate disposal. 

Other Considerations Leakage of cold air into a settling chamber can cause local gas quenching and condensation. Condensation can cause corrosion, dust buildup, and plugging of the hopper or dust removal system. The use of thermal insulation can reduce heat loss and prevent condensation by maintaining the internal device temperature of the above the dew point (EPA, 1982). No pretreatment is necessary for settling chambers. 

The term three-phase fluidization requires some explanation, as it can be used to describe a variety of rather different operations. The three phases are gas, liquid and particulate solids, although other variations such as two immiscible liquids and particulate solids may exist in special applications. As in the case of a fixed-bed operation, both co-current and counter- current gas-liquid flow are permissible and, for each of these, both bubble flow, in which the liquid is the continuous phase and the gas dispersed, and trickle flow, in which the gas forms a continuous phase and the liquid is more or less dispersed, takes place. A well established device for countercurrent trickle flow, in which low-density solid spheres are fluidized by an upward current of gas and irrigated by a downward flow of liquid, is variously known as the turbulent bed, mobile bed and fluidized packing contactor, or the turbulent contact absorber when it is specifically used for gas absorption and/or dust removal. Still another variation is a three-phase spouted bed contactor. 

As a simple and efficient particle separation device, cyclone collectors can be used for anything from dust removal in a fluid stream to material collection in the fluid conveying system. However, the cyclone is not suitable or economical for the separation of extremely small particles (say, less than 1 /xm), which frequently occur in industrial processes. It is recommended that the size of particles to be separated in an industrial ventilation cyclone be in the region of around 10 to 100 p.m. However, for the purpose of aerosol sampling, the size of particles to be separated may be much less than 10 jxm. 

The basic operations performed by dust-collection devices are (1) separating particles from the gas stream by deposition on a collection surface, (2) retaining the deposited particles on the surface until removal, and (3) removing the deposit from the surface for recovery or disposal. 

In spite of a few minor operating problems, the DSHS tests appeared to have been successful. All materials, pallets, carbon, and DPE suit material were reduced to the size specified for feeding to the SCWO system the metal removal devices appear to have performed well, and fugitive dust appears to have been controlled. The size reduction of the DPE suit material was of special interest because the technology for heavy polymeric composites is comparatively new. 

The majority of these units have a Third Stage Separator (TSS) or electrostatic precipitator (ESP) located before the SCR catalyst bed to protect against upsets in the FCC regenerator. The catalyst can easily be designed to handle the normal dust loading (60 mg-700 mg/Nm ), which is much lower than the typical coal fired boiler (5 g-9 g/Nm ). To handle a FCC upset (>15 g/Nm ) without a PM removal device, the catalyst volume would need to increase. 

If ultrafme particles can be agglomerated, the mass of the new entity is equal to the sum of aU particles in the structure and mass related forces as well as inertia increase proportionately. After agglomeration, ultrafine particles, in their new form, can be removed in standard dust collection devices such as cyclones and packed bed filters. 

Sand blasting of the surface may be permitted if sufficient personal protective devices and ventilation by Forced Draught (FD) fans, dust removal Induced Draught (ID) fans are used. However, workers should not enter the vessel when this is being done. 

The most commonly used inertial collector is the cyclone (Fig. 5.6). This consists of a cylindrical vessel into which the gas stream is introduced tangentially. The rotational motion of the gas stream causes movement of the particles to the outer wall where deposition and aggregation occur. The dust falls to the base of the cyclone and is removed into a hopper, whilst the cleaned gas stream is removed at the top. The main disadvantage of the cyclone, and of other inertial collectors, is the low efficiency at small particle sizes, and for this reason the cyclone is most commonly used to pre-clean an air stream which is subsequently polished using a more efficient dust arresting device. 

Cyclones These are usually used as intermediate dust control devices by various process industries, particularly in pneumatic conveying. They are rarely used as the final devices due to their low efficiency characteristics for removal and recovery of small particle sizes below approximately 10 microns. When ambient air regulations call for controlling dust above 10 microns (e.g. PM 10) some industries (e.g. wood working, construction and municipal) use cyclones as the final dust control step.. 

Bubbling—the vortical device is supposed to mount in vent dust removal systems with the purpose of economy of the areas of industrial premises, thus hydraulic resistance of system does not exceed 500 Pa, power inputs on clearing of gas in 3 times below, than in known devices. 

Polonium can be mixed or alloyed with beryllium to provide a source of neutrons. The element has been used in devices for eliminating static charges in textile mills, etc. however, beta sources are both more commonly used and less dangerous. It is also used on brushes for removing dust from photographic films. The polonium for these is carefully sealed and controlled, minimizing hazards to the user. 

Other Centrifugal Collectors. Cyclones and modified centrifugal collectors are often used to remove entrained Hquids from a gas stream. Cyclones for this purpose have been described (167—169). The rotary stream dust separator (170,171), a newer dry centrifugal collector with improved collection efficiency on particles down to 1—2 pm, is considered more expensive and hence has been found less attractive than cyclones unless improved collection in the 2—10-pm particle range is a necessity. A number of inertial centrifugal force devices as well as some others termed dynamic collectors have been described in the Hterature (170). 

Cement plants in the United States are now carehiUy monitored for compliance with Environmental Protection Agency (EPA) standards for emissions of particulates, SO, NO, and hydrocarbons. AH plants incorporate particulate collection devices such as baghouses and electrostatic precipitators (see Air POLLUTION CONTROL methods). The particulates removed from stack emissions are called cement kiln dust (CKD). It has been shown that CKD is characterized by low concentrations of metals which leach from the CKD at levels far below regulatory limits (63,64). Environmental issues continue to be of concern as the use of waste fuel in cement kilns becomes more widespread. 

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